The code here didnt work for classic template on prestashop 1.7.4.3, I used this code instead:
{block name='product_flags'} <ul class="product-flags"> {if $product->quantity == 0 AND $quantity == 0} <li class="product-flag"> {l s="NOT AVAILABLE" d="Shop.Theme.Catalog"} </li> {/if} {foreach from=$product.flags item=flag} <li class="product-flag {$flag.type}">{$flag.label}</li> {/foreach} </ul> {/block}
But just coudlt quite get the main page to show the label..